docs: def _validate_hue(df, hue):
      """
      The top-level ``hue`` parameter present in most plot types accepts a variety of input types. This method
      condenses this variety into a single preferred format---an iterable---which is expected by all submethods working
      with the data downstream of it.
  
      Parameters
      ----------
      df : GeoDataFrame
          The full data input, from which standardized ``hue`` information may need to be extracted.
      hue : Series, GeoSeries, iterable, str
          The data column whose entries are being discretely colorized, as (loosely) passed by the top-level ``hue``
          variable.
      required : boolean
          Whether or not this parameter is required for the plot in question.
  
      Returns
      -------
      hue : iterable
          The ``hue`` parameter input as an iterable.
      """
      if hue is None:
          return None
      elif isinstance(hue, str):
          hue = df[hue]
          return hue
      else:
          return gpd.GeoSeries(hue)